“This would never happen on a normal lake, because a normal lake is knowable. A Great Lake can hold all the mysteries of an ocean, and then some.” 

In the book’s Introduction, the author sets up the expectation that the Great Lakes are a highly unusual body of water that don’t conform to normal expectations of what a lake should be—an idea which eludes those individuals who believe they can control the Lakes. Just as people struggle to understand the depths of the ocean, they struggle to understand all the mysteries of the Great Lakes. 

“The folly here is that ballast water isn’t just water. It swarms with perhaps the most potent pollutant there is: DNA.” 

Although water carried through the hulls of overseas ships may not seem like a great threat at first, Egan quickly dispels this notion. The DNA of these non-native creatures arriving on these ships will irrevocably alter the Great Lakes.

“These ships are like syringes.” 

Egan's use of literary devices like simile help illustrate the significant threat that these overseas ships pose to the Great Lakes. Like a syringe, they suck in various sea creatures and then shoot them out into the Great Lakes, changing the landscape.